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then link-state advertisements (LSA) will be sent among neighboring layer3 switches.
Neighboring layer3 switch copy the LSA to their routing table and transfer the information
to the rest part of the network. This process is referred to as “flooding”. In this way,
firsthand information is sent throughout the network to provide accurate map for creating
and updating routes in the network. Link-state routing protocols use cost instead of hops
to decide the route. Cost is assigned automatically or manually. According to the
algorithm in link-state protocol, cost can be used to calculate the hop number for
packages to pass, link bandwidth, and current load of the link, The administrator can
even add weight for better assessment of the link-state.
1) When a link-state layer3 switch enters a link-state interconnected network, it
sends a HELLO package to get to know its neighbors and establish neighborhood.
2) The neighbors respond with information about the links they are connecting and
the related costs.
3) The originate layer3 switch uses this information to build its own routing table.
4) Then, as part of the regular update, layer3 switch send link-state advertisement
(LSA) packages to its neighboring layer3 switches. The LSA include links and related
costs of that layer3 switch.
5) Each neighboring layer3 switch copies the LSA package and passes it to the next
neighbor (i.e. flooding).
6) Since routing database is not recalculated before layer3 switch forwards LSA
flooding, the converging time is greatly reduced.
One major advantage of link-state routing protocols is the fact that infinite counting is
impossible, this is because of the way link-state routing protocols build up their routing
table. The second advantage is that converging in a link-state interconnected network is
very fast, once the routing topology changes, updates will be flooded throughout the
network very soon. Those advantages release some layer3 switch resources, as the
process ability and bandwidth used by bad route information are minor.
The features of OSPFv3 protocol include the following: OSPFv3 supports networks
of various scales, several hundreds of layer3 switches can be supported in an OSPFv3
network. Routing topology changes can be quickly found and updating LSAs can be sent
immediately, so that routes converge quickly. Link-state information is used in shortest
path algorithm for route calculation, eliminating loop route. OSPFv3 divides the
autonomous system intro areas, reducing database size, bandwidth occupation and
calculation load. (According to the position of layer3 switches in the autonomous system,
they can be grouped as internal area switches, area edge switches, AS edge switches
and backbone switches). OSPFv3 supports load balance and multiple routes to the same
destination of equal costs. OSPFv3 supports 4 level routing mechanisms (process routing
according to the order of route inside an area, route between areas, first category
